This application claims the priority of German patent application 197 23 878.5, filed Jun. 6, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a heat exchanger comprising several flat tubes whose open ends are widened for forming sections of the coolant tanks and by means of contact surfaces having passage openings are placed directly on adjacent flat tubes and are provided with a tight closure on the open side.
Heat exchangers of this type of construction are known from German Patent Document DE-A 36 22 953 or from German Patent Document DE-A 37 01 865. In these known constructions, the tube ends are bent open to form approximately rectangular tanks and their larger lateral surfaces are provided with passage openings so that, when the flat tubes are placed against one another with their widened end sections, they leave a space between one another for receiving fin lamellae. These constructions avoid the otherwise required insertion of intermediate rings between the tube ends (European Patent Application EP-A 01 06 479) and therefore permit a relatively simple construction of the initially mentioned heat exchangers. In the known constructions, the open sides of the bent-open end tanks of the flat tubes were in each case closed by inserted covers so that in this manner, after the adjoining of the flat tubes, a continuous coolant tank is formed and, on the other hand, it is ensured that the bent-open tanks at the end of the flat tubes are dimensionally stable and do not lose the parallelism of the contact surfaces with the passage openings.
It is an object of the invention to further simplify the construction of heat exchangers of the above-mentioned type. According to the invention, this and other objects have been achieved in that, in the case of a heat exchanger of the initially mentioned type, the tight closure of the open tube ends is formed by wall parts of the flat tube ends which project beyond the contact surfaces and which are folded back to the inside, are placed against one another and are connected with one another.
This further development is based on the recognition that the additional arrangement of covers for closing off the bent-open tube ends can be eliminated if the bent-open area is constructed to be much larger than previously and the wall parts which project beyond the area of the contact surfaces with the passage openings are then used for forming the closure. This consideration departs from the previous opinion that a bending-open of flat tubes, because of the connected danger of a tearing of the tubes as the result of the expansion of the material, be constructed as short as possible or just as long as required. This therefore leads to the advantage that cover parts, which must be manufactured separately, must no longer be provided as the closure of the bent-open areas. The invention also eliminates the existing fear that the dimensional accuracy of the contact surfaces later to be placed against adjacent flat tubes, particularly their parallel alignment, may be disadvantageously influenced by the deformation of the wall parts adjoining the contact surfaces. It was found that the tight closing can be carried out by the corresponding wall parts of the longer bent-open area without any disadvantageous effect on the dimensions of the areas later to be placed against one another to form the coolant tank.
In a further development of the invention, the wall parts projecting beyond the contact surfaces may have a length which corresponds to at least half the width of the sections of the coolant tanks, optionally plus the dimension required for an overlapping or fold formation. As will be explained below, this further development makes it possible to produce the heat exchangers according to the invention in different fashions. Specifically, the projecting wall parts may be buckled toward the inside by approximately 90.degree. and obtusely placed against one another and connected with one another, particularly welded to one another. However, it is also possible to construct the wall parts still longer, to let them overlap after the buckling and to connect them in this form. In both cases, the folds of the exterior wall formed on the narrow lateral surfaces of the bent-open end tanks of the flat tubes can be folded over and into the surface of the assigned side of the widened tank-shaped bent-open area.
Naturally, it is also possible to fold the projecting wall parts toward the inside, to place them flatly against one another approximately in the center plane of the flat tubes and then to shape them into a tight fold, which is known per se in the case of other developments of heat exchangers (European Patent Document EP 04 44 595 B1).
The invention also relates to a process for manufacturing the flat tubes for the heat exchanger according to the invention and provides in a first embodiment that, for manufacturing a flat tube, as outlined in the claim, the wall parts projecting over the contact surfaces, while buckling out the exterior walls of the widened area which extend transversely to them, are placed against one another, are optionally folded over to form a fold and are then connected. As a further development of this inventive idea, it was found to be very expedient that the wall parts, which before being placed against one another and folded, were buckled to the inside, are, in addition, buckled along a straight line extending in parallel to the end edge such that the end sections will again extend to the outside. As a further development of the invention, the parts, which point to the outside from the bend, are then placed flatly against one another and folded over to form the fold.
For producing another type of a tight closure, however, according to the invention, the wall sections can also first be bent by 90.degree. and can then be placed obtusely against one another with their free edges and welded together, in which case, as explained above, the exterior wall parts which extend transversely to them are buckled to the outside and can then be folded into the surface of the widening.
Finally, it is also possible to buckle the wall parts by approximately 90.degree. and to place them with their ends in an overlapping manner on one another. Also in this case, the exterior wall parts, which extend transversely to them, are buckled toward the outside and folded into the surface of the tank-shaped widening.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.